Treatment of iron ores containing nickel and chromium



3,141,704 Patented July 21, 1964 TREATMENT OF IRQN QRE CGNTAINING NIQKELAND CHRUMTUM Kiyoto Matsuzulra, Junjiro Momozalti, and YoshinoriShirane, Kumamoto, Japan, assignors to Yawata Iron and Steel (30., Ltd,Tokyo, Japan No Drawing. Filed Dec. 28, 1960, er. No. 78,817 (Ilairnspriority, application Japan Feb. 15, 1960 2 Ciairns. (Cl. 75-82) Thisinvention relates to a process for the separation of nickel from ironores containing nickel and chromium by which the nickel content isseparated and removed therefrom, and more particularly, relates to atreatment in which the nickel content is extracted by the steps whichcomprises treating the iron ore containing nickel and chromium which hasbeen already roasted for reduction with a dilute sulphurous acidsolution, and then separating iron and nickel in this leach solution.

Heretofore, of the important iron ores containing nickel and chromium,an essential and major one has been called laterite, which has beenreported to have vast reserves all over the world, but, at present, itis not suitable for a raw material for iron or steel manufacture,because it contains a substantial amount of alumina as well as a smallamount of nickel and chromium. In reference to the separation andremoval of the nickel and chromium content, innumerable researches havebeen conducted and many patents have been granted. Of processes forremoving the nickel content by extraction, the treatment of the oreroasted for reduction with a sulphuric acid is generally used, but, bythis method, a considerable amount of iron as well as the nickel contentis leached. Therefore, the iron content should be separated from thenickel content for recovery of iron. As the leached iron content isconverted into ferrous sulphate and ferric sulphate, it is consideredthat the oxidation of the ferrous sulphate into ferric sulphate with aview to removing the iron is very difiicult, because this oxidationrequires an elevated temperature, a high pressure, and an extendedperiod of time. It is also reported that with the progress of oxidationas the concentration of sulphuric acid in the liquor increases, the rateof oxidation rapidly decreases (see, for example, K. A. Kobe and W.Dickey: Ind. Eng. Chem, vol. 37, 1, 1945).

This invention contemplates the provision of a treatment process whichhas solved the above disadvantage. In accordance with the process ofthis invention, instead of sulphuric acid a dilute sulphurous acid isused to extract the nickel content from the ore containing nickel andchromium which has been subjected to a reducing roast, by which the ironcontent dissolved in the leach liquor is maintained as low as possible,and this iron is easily separated from nickel to recover it by a simpletreatment such as air blowing.

It is an'object of this invention to provide a process for treating theiron ore containing nickel and chromium in order to remove the nickelcontent in a most economical and commercial manner.

Another object of the invention is to provide a treating process inwhich the iron content dissolved in the leach liquor resulting from theextraction of the nickel content from the iron ore containing nickel andchromium is completely recovered with the separation of nickel.

A further object of the invention is to provide a treating process inwhich chromium is easily and elfectively removed by adding soda ash andlime to a magnetite ore resulting from the residue and roasting it in anoxidizing atmosphere, said magnetite ore being obtained from the residueresulting from the extraction of nickel by subjecting the iron orecontaining nickel and chromium to the abovementioned reducing roasttreatment and then to leaching it with the dilute sulphurous acidliquor, and

said roasted ore being accessible to the removal of chrom-' ium due toits magnetite form.

A In accordance with the process of this invention, the lateritic ironore, which constitutes the major part of balt are extracted, andfurther, the separation of nickel from iron is effected by an airblowing process.

In a conventional leach process for extracting the nickel content fromgarnierite ore, the latter is subjected to a leach with sulphurous acidliquor after the reducing roast, but, in general, as this processrequires a concentrated sulphurous acid, a substantial amount of iron isalso leached together with nickel.

As is well known, laterite ore usually contains cobalt in an amountcorresponding to about 10% of the nickel contained in the ore, andusually cobalt behaves similarly to nickel. Accordingly, the extractionof nickel will also include extraction of cobalt, whenever the latter ispresent in the ore.

However, we have discovered after an extensive study by means of X-raythat the nickel content of the lateritic ore contains no garnieritewhatever, but all of it exists in the form of an oxide. Accordingly, ithas been found that laterite is more easily reducible than garnieriteand also can be leached with a very dilute sulphurous liquor.

Thus, we can attain over of the extraction efficiency of nickel withsuch a dilute sulphurous liquor as in the order of 0.5% to 5%, andpreferably 0.5 %+3% by weight of S0 after having subjected laterite tothe reducing roast, and in addition, we can inhibit an amount of leachediron to less than 10% iron, which is also leached together with nickel,but undesirable. This finding is most significant to industry and hasadvantages enumerated below:

(1) As the extraction of iron is maintained to the extent of 5 to 10%,to of the iron content contained in the laterite can be obtained as amagnetite ore containing no nickel whatever.

(2) An amount of dissolved iron and impurities other than nickel in thenickel leach liquor is considerably less than that of prior art, so thesubsequent processing of the liquor is not difiicult.

(3) As the liquor consists of a dilute solution of sulphurous acid, itis easy to prevent the loss resulting from evaporation during theoperation step.

(4) The wear caused by the corrosion of the equip ment due to thesulphurous acid liquor can be reduced.

Examples showing the above process consisting of leaching the lateritesubjected to a reducing roast with a dilute sulphurous acid liquid aregiven hereinbelow.

EXAMPLE 1 Laterite of chemical analysis of 50.5% Fe, 1.21% Ni, 2.07% Cr,6.40% A1 0 and 3.3% SiO crushed to the fineness of --30 mesh isthoroughly mixed with 5% pulverized coal of -48 mesh added thereto, andthe resultant material is charged into a rotary kiln (its inner diameterbeing 15 cm., its length, 400 cm.; one revolution per minute; itsinclination, to be reduced by an incomplete combustion with a coal gas.Nickel is extracted from the above reduced ore with the use of variousconcentrations, percent S0 by weight, and at the same time, iron is alsoextracted with the determination of its extraction rate, respectively.The results are shown in Table 1 wherein the rate of reduction is theamount of reduced metal, principally iron, in the reduced ore calculatedin percent of the Weight of the total content of reducible metal (iron)in the unroasted ore; and wherein the rate of extraction 3 is the amountof iron or nickel, respectively, in solution calculated in percent ofthe amount of the respective metal in the unleached ore.

Table 1 Samples Extracting conditions Rates of extraction Reduc- RateS02, Solu- Agita- Coning of pertion ting cen- Ni, Fe, temperreduccenttemtime, tration perperpertion y perminof pulp cent cent ature(perweight ature, utes by cent) 0. weight Table 1 shows that the rate ofextraction of nickel will amount to 80 to 86%, and that of iron to to atthe concentration of 0.5 to 3% S0 by weight of dilute sulphurous acid.

In order to remove chromium from the residue magnetite, which is addedwith soda ash and 10% slaked lime, and then, formed into pellets by adisk-type balling device. These pellets are roasted in a down-draftsinter machine at the temperature of 1000 C. for the period of one hour.When the roasted pellets are leached in the hot water of the temperatureof 70 C. for the period of two hours, the rate of extraction of chromiumhas amounted to 90.0%.

Now, the recovery of iron from the nickel leach liquor will be describedhereinafter.

In general, when the iron ore containing nickel is treated withsulphuric acid, iron is converted into ferrous and ferric sulphate.However, the oxidation of ferrous sulphate into ferric sulphate in orderto remove iron therefrom is very diflicult as described hereinbefore.

However, in the process of this invention, as the laterite roasted forreduction is leached with the dilute sulphurous acid liquor, most ofiron and nickel in the resultant leach liquor is of primary sulphite.If, then, ferrous sulphite in the iron content is once oxidized intoferrous sulphate, the oxidation of the latter into ferric sulphate inorder to remove iron therefrom is extremely hard as evident from theforegoing.

Accordingly, the invention contemplates the attainment of two objects,removal of sulphur as well as iron and prevention of increase of acidconcentration in the leach liquor, by the process which comprisespermitting no oxidation to occur from ferrous sulphite to ferroussulphate but removing iron immediately without delay. The processreferred above consists in removing free S0 from the nickel leach liquorresulting from the above-mentioned dilute sulphurous acid liquor byvacuum distillation, and thereafter agitating the resultant liquor, thecolor of which turns into reddish brown, which shows that ferroussulphite is oxidized into ferric sulphite as follows:

Literature shows that this ferric sulphite is an unstable compound,which tends to become ferrous sulphate immediately if left untouched.

The feature of the invention lies in the process which comprisessubjecting ferric sulphite to decomposition without delay in such mannerthat the oxidation of ferric sulphite to ferrous sulphate will not takeplace. This is accomplished by a simple commercial process whichcomprises heating the leach liquor to a temperature of 60 to 4, 100 C.while blowing air thereinto, and this reaction is shown as follows:

heat 1 FG3(SO3)3 O; Basic ierlrie sulphate S02 By heating the leachliquor and oxidizing it by blowing in air, the ferric sulphite isdecomposed into basic ferric sulphate and S0 More particularly, achemical reaction by which S0 is separated in the above decompositioncontributes not only the recovery of S0 but also the prevention of anincrease of acid concentration. This con tribution is particularlysignificant.

This simple process consisting of blowing air thereinto Whiledecomposing the ferric sulphite by heating it to a temperature of 60 to100 C. is an important factor to industry.

By a mechanical agitation or stirring only without recourse to airblowing, several steps of filtration from the precipitate and anextended period of heating time therefor are required before thedecomposition is completed. However, on the contrary, by the air blowingprocess, a comparatively short period of time at a time is adequate toattain the desired results. Furthermore, in the air blowing process, thecontact area of air with liquid Will be improved by forming a number offine foams, which will result in a reduced period of time. In addition,the combined action of agitation and air blowing will accelerate thedecomposition.

A process of removing sulphur and iron resulting from the decompositionof ferric sulphite by the above air blowing step will be referred to asair de-ironization, in this invention.

By the application of the above process, prior to an autoclave treatmentof the leach liquor under a high temperature and a high pressure with aview to removing iron therefrom, the removal of the major part ofsulphur and iron can be effected at an intermediate step in avery simplemanner, hence the final autoclave treatment step can be carried out inan easier and more complete manner than heretofore.

' An example showing the above process of air de-ironization will bedescribed hereinbelow:

EXAMPLE 2 Experiment results of air de-ironization combined withmechanical agitation conducted on the dilute sulphurous acid leachliquor (extraction rate: 84.3% Ni and 9.53% Fe) of the reduced lateriticore of chemical analysis mentioned he'reinbefore are shown in Table 2:

Table 2 Vacuum- Preclpi- Precipi- Ingredient Leach distilled tatefiltate filliquor liquor trate, trate,

primary secondary Fe(g./l.) 2. 14 2. 12 1. 72 0. or T 4. 64 2. 52 2.31 1. 06 0. 59 0. 59 0. 60 1. 02 2 5.1 4.7 1.8

When the leach liquor is subjected to vacuum distillation, free S0 isremoved. Next, the resultant liquor is agitated while heated at thetemperature of C. with the result that basic iron sulphate isprecipitated while S0 is being evaporated off. The resultant precipitateis filtered. This operation is repeated again and again until the ironcontent in the leach liquor is 0.91 g./l., the total S 1.06 g./l., and Sof 80.; 1.02 g./l., which shows that the rate of de-ironization (ironremoval) amounts to 57.5% and the rate of desulphurization to 77.0%.This means the desulphurization has reached its end point, and theperiod of time required for agitation has amounted to three hours.

Table 3 present in the ore are extracted from the leach liquor by theautoclave treatment. Blowing time 30 minutes 60 minutes In process B,the precipitate of basic iron sulphate produced by the airde-ironization process as it is together Leach P ecipi. Leach precipi. 5with the leach liquor is subjected to an autoclave treat- Ingredientliquor te g ilr liquor rnent. Then, the precipitate separated byfiltration is calcined to give iron oxide, and simultaneously, a nickelor 2 0 71 2 62 0 38 nickel-cobalt solution is obtained. 1 1 02 1 It willbe understood that the above two processes are i: i i12 13 9:3 10eliective. Further, in case a very small quantity of free sulphurousacid is produced in carrying out an extracting operation with a dilutesulphurous acid liquor, a vacuum 1i 52 32:2 2 s: s? yg i ig the same 1distillation step may be omitted in both processes. ogheating it s giggig i is g i An example of the eiiect obtained from the combined P P e 9W l e .owlng 15 process of air de-ironization and autoclave treatment isarr mto it by a blower. When an blowing is carried out a shownherembelow. for a period of 30 minutes, the rate of de-ironization 1864.5% while that of desulphurization 78.3%, and for a EXAMPLE 3 periodof one hour, the de-ironization 85.5% while the desmphurization 7 3%When the air de-rronrzatron process is carried out prior It is clear fthe results f the above examples that 20 to the high pressure treatmentby an autoclave, the actual the air blowing process is more effectivethan the mechanieficts lmpartlng to the autoclave treatment are shown Incal agitation. Table 4 as follows:

An analysis of the basic iron sulphate precipitated by Table 4 the aboveprocess and dried at the temperature of 100 C. shows that it consists of48.3% Fe, 5.99 S and 3 22% Prior to Priorto Aim applmw ignition loss.When this iron sulphate 1s calcined in acapplication of applioatitzntogtlion oiilprfissure, a ressure, Fe pressure, 0 a ein e quor cordanceWith the first process described herernbefore, 1t thenquor sintheuquor,gJL is found that it consists of hematite containing 5.30% g [l ./1 A1 0and it is a good raw material for iron manufacture with traces of nickeland chromium. 3. 7 6,6 are In carrying out the air de-ironizationprocess, it is con- Z-g fig 8 sidered that there are two processescombined with an 1:6 2.0 0.08 autoclave treatment, the flowsheets ofwhich are shown hereinbelow:

PROCESS A 30: S09 e l l 02 t 1. Ni vacuum air 02 (air)defiltraautofiltra- Ni, 00 leach distilironization tion clave tronsolution liquor lation l basic ferric sulphlte S02 calcination ironoxide PROCESS 13 S02 S02 F'W i 01 Ni vacuum air deauto filtra- Ni, Coleach distilirom'zation clave tion solution liquor lation S02calornation iron oxide In process A, the precipitate of basic ironsulphate produced by the air de-ironization process is separated byfiltration and the filtrate is subjected to an autoclave treatment. Whenthe precipitate is calcined, sulphurous acid gas is produced. At thesame time when the sulphurous acid gas is recovered, iron oxidecontaining no nickel and chromium is obtained, which is suitable for araw material for iron manufacture.

Nickel and cobalt where such is 75 The treating conditions by theautoclave are: the partial pressure of oxygen is 5 kg./cm. the totalpressure thereof 20 kg./cm. the temperature 210 C., and an operatingtime 2 hours. When the air de-ironization is carried out prior to theautoclave treatment, it has been found out that the autoclave treatmentcan be performed to advantage. When the leach liquor containing 8.7g./l. Fe and 6.6 g./l. total S is treated under pressure, Fe is 0.18g./l.

7 while, on the other hand, Fe is reduced to 0.06 g./l., almostone-third thereof, by the same high pressure treatment which has beenperformed on the leach liquor containing 12 g./1. Fe and 1.7 g./l. S,the amounts of Fe and S, respectively, have been adjusted by the airdeironization process.

Furthermore, when the basic ferric sulphite precipitated by the airde-ironization process is subjected to the autoclave treatment withoutbeing separated by filtering in the above described process B, and theprecipitate is then separated by filtering, and dried at the temperatureof 100 C., the chemical analysis of the resultant product is 53.9% Fe,12.6% S and 12.6% ignition loss. The analysis of this precipitate isclose to that of Fe O -H O. Therefore it is easy to filter and separateit from precipitate. When calcined, it serves as an excellent rawmaterial containing neither nickel nor chromium for iron manufacture.

We claim:

1. A process for treating a laterite iron ore, in finely divided form,containing nickel and chromium which comprises subjecting said ore to areducing roast, leaching the roasted ore with dilute sulfurous acidcontaining about 0.5 to 3% by weight of S0 whereby nickel as well ascobalt, when the latter is present in the ore, and 510% of the ironcontained in said ore are leached out, the leached iron being in theform of ferrous sulfite in the resultant leach liquor, while thechromium remains in the ore, agitating said liquor whereby ferroussulfite is converted to ferric sulfite, immediately blowing air intosaid leach liquor while heating the latter to a temperature of to C.thereby decomposing said ferric sulfite to ferric sulfate and S0 andseparating the precipitated ferric sulfate from the remaining liquor.

' 2. A process for treating a laterite iron ore, in finely divided form,containing nickel and chromium which comprises subjecting said ore to areducing roast, leaching the roasted ore with dilute sulfurous acidcontaining about 0.5 to 3% by weight of S0 whereby nickel as well ascobalt, when the latter is present in the ore, and 510% of the ironcontained in said ore are leached out, the leached iron being in theform of ferrous sulfite in the resultant leach liquor, while thechromium remains in the ore, vacuum distilling to remove excess S0present in said liquor, agitating said liquor whereby ferrous sulfite isconverted to ferric sulfite, immediately blowing air into said leachliquor while heating the latter to a temperature of 80 to 100 C. therebydecomposing said ferric sulfite to ferric sulfate and S0 and separatingthe precipitated ferric sulfate from the remaining liquor.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR TREATING A LATERITE IRON ORE, IN FINELY DIVIDED FORM,CONTAINING NICKEL AND CHROMIUM WHICH COMPRISES SUBJECTING SAID ORE TO AREDUCING ROAST, LEACHING THE ROASTED ORE WITH DILUTE SULFUROUS ACIDCONTAINING ABOUT 0.5 TO 3% BY WEIGHT OF SO2, WHEREBY NICKEL AS WELL ASCOBALT, WHEN THE LATTER IS PRESENT IN THE ORE, AND 5-10% OF THE IRONCONTAINED IN SAID ORE ARE LEACHED OUT, THE LEACHED IRON BEING IN THEFORM OF FERROUS SULFITE IN THE RESULTANT LEACH LIQUOR, WHILE THECHROMIUM REMAINS IN THE ORE, AGITATING SAID LIQUOR WHEREBY FERROUSSULFITE IS CONVERTED TO FERRIC SULFITE, IMMEDIATELY BLOWING AIR INTOSAID LEACH LIQUOR WHILE HEATING THE LATTER TO A TEMPERATURE OF 80 TO100*C. THEREBY DECOMPOSIG SAID FERRIC SULFITE TO FERRIC SULFATE AND SO2,AND SEPARATING THE PRECIPITATED FERRIC SULFATE FROM THE REMEININGLIQUOR.